Method and system for cooling a motor during motor startup

ABSTRACT

A HVAC system includes a compressor having a low pressure input and a high pressure output. The compressor is driven by a motor having a liquid coolant flowpath configured to cool and lubricate the motor. The motor has a coolant input and a coolant output. An evaporator is in communication with the compressor, and includes a coolant input and a coolant output. A condenser is in fluid communication with the evaporator and the compressor. A first coolant flowpath, includes a coolant drive system connecting the output of the condenser to a valve switching device. A second coolant flowpath connects the output of the condenser to the input of the evaporator and to a second input of the valve switching device. A third coolant flowpath connects the valve switching device to the inputs of the motor. A fourth coolant flowpath connects outputs of the motor to the input of the evaporator.

TECHNICAL FIELD

The present disclosure relates generally to compressor motor cooling and lubrication, and more specifically to compressor motor cooling and lubrication during a startup sequence.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application No. 62/740,476 filed on Oct. 3, 2018.

BACKGROUND

Global warming and other environmental concerns have lead the heating, ventilation and cooling (HVAC) industry to explore alternative low Global Warming Potential (GWP) refrigerants in place of existing refrigerants in HVAC systems. However, due to their low pressure characteristics, some low GWP refrigerants, especially those suitable for use in small capacity systems such as rooftops and residential systems, require the utilization of a high-efficiency compressor, evaporator and condenser.

Certain high-efficiency compressors, such as high speed centrifugal compressors, require a high speed motor for proper operation. High speed motors, however, require that the motor bearings be cooled and lubricated via a cooling system in order to keep the motor system below a limitation temperature and prevent the bearings from overheating. Traditional air cooling of such systems can be inadequate for a high speed motor, and independent oil based liquid cooling leads to complex systems and increases costs.

SUMMARY OF THE INVENTION

In one exemplary embodiment a heating ventilation and air conditioning (HVAC) system includes a compressor comprising a low pressure input and a high pressure output, the compressor driven by a motor, the motor including a liquid coolant flowpath configured to cool and lubricate the motor and having a liquid coolant input and a liquid coolant output, an evaporator in fluid communication with the compressor, the evaporator including a liquid coolant input, and a vapor coolant output, the vapor coolant output being connected to the low pressure input of the compressor, a condenser in fluid communication with the evaporator and the compressor, the condenser including a vapor cooling input and a liquid coolant output, the vapor cooling input being connected to a high pressure output of the compressor, a first liquid coolant flowpath, including a liquid coolant drive system connecting the liquid coolant output of the condenser to the input of a valve switching device, a second liquid coolant flowpath connecting the liquid coolant output of the condenser to the liquid input of the evaporator and to a second input of the valve switching device, a third liquid coolant flowpath connecting an output of the valve switching device to the liquid coolant inputs of the motor, and a fourth liquid coolant flowpath connecting the liquid coolant outputs of the motor to the liquid coolant input of the evaporator.

In another example of the above described heating ventilation and air conditioning (HVAC) system the liquid coolant drive system comprises an electric pump.

In another example of any of the above described heating ventilation and air conditioning (HVAC) systems the electric pump is disposed within a reservoir integrated into the condenser.

In another example of any of the above described heating ventilation and air conditioning (HVAC) systems the electric pump is disposed within a reservoir exterior to the condenser.

In another example of any of the above described heating ventilation and air conditioning (HVAC) systems the electric pump is disposed outside of the condenser.

Another example of any of the above described heating ventilation and air conditioning (HVAC) systems further includes a controller controllably connected to the three way valve, the electric pump and the motor.

In another example of any of the above described heating ventilation and air conditioning (HVAC) systems the controller is configured to activate the electric pump at least five seconds prior to activating the motor.

In another example of any of the above described heating ventilation and air conditioning (HVAC) systems the liquid coolant drive system comprises a liquid coolant reservoir.

In another example of any of the above described heating ventilation and air conditioning (HVAC) systems the liquid coolant reservoir is disposed above the motor, relative to a force of gravity, such that a liquid coolant is gravity fed from the reservoir to the motor when the valve switching device is in a first state.

In another example of any of the above described heating ventilation and air conditioning (HVAC) systems the liquid coolant reservoir includes an electric heater disposed within the liquid coolant reservoir.

In another example of any of the above described heating ventilation and air conditioning (HVAC) systems the electric heater is controllably coupled to a controller, and the controller is configured to activate the electric heater at least 5 minutes prior to activating the motor.

Another example of any of the above described heating ventilation and air conditioning (HVAC) systems further includes a one way valve disposed in the first liquid coolant flowpath between the liquid coolant output of the condenser and the input to the reservoir, and oriented such that liquid coolant flows from the condenser to the reservoir and is prevented from flowing from the reservoir to the condenser.

In another example of any of the above described heating ventilation and air conditioning (HVAC) systems the liquid coolant flowpath includes a liquid phase R1233zd(E) (CHCl=CH=CF3) refrigerant.

In another example of any of the above described heating ventilation and air conditioning (HVAC) systems the second liquid coolant flowpath includes an expansion device connecting the liquid coolant output of the condenser to the liquid input of the evaporator.

In another example of any of the above described heating ventilation and air conditioning (HVAC) systems the first liquid coolant flowpath includes a check valve connecting the liquid coolant output of the condenser to the liquid coolant drive system.

An exemplary method for operating a heating ventilation and air conditioning (HVAC) system includes driving a liquid coolant from a condenser to a compressor motor during a startup sequence of the compressor motor using a liquid coolant drive system, thereby cooling and lubricating the compressor motor, and drawing liquid coolant from the condenser to the compressor motor using a pressure differential between the condenser and an evaporator once the startup sequence has completed.

In another example of the above described exemplary method for operating a heating ventilation and air conditioning (HVAC) system driving the liquid coolant comprises providing liquid coolant from the condenser to a reservoir and heating the liquid coolant in the reservoir, thereby increasing a pressure of the liquid coolant.

In another example of any of the above described exemplary methods for operating a heating ventilation and air conditioning (HVAC) system driving the liquid coolant comprises operating an electric pump disposed within the condenser.

In another example of any of the above described exemplary methods for operating a heating ventilation and air conditioning (HVAC) system driving the liquid coolant comprises operating an electric pump disposed between an outlet of the condenser and a liquid coolant inlet of the compressor motor.

Another example of any of the above described exemplary methods for operating a heating ventilation and air conditioning (HVAC) system further includes transitioning from driving the liquid coolant using the liquid coolant driving system to drawing liquid coolant from the condenser to the compressor motor using a pressure differential between the condenser and the evaporator in response to the compressor motor exceeding a rotational speed.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a high level schematic view compressor motor cooling system for a high speed motor for a heating, ventilation and air condition (HVAC) system.

FIG. 2 schematically illustrates a variation of the configuration of FIG. 1.

FIG. 3A schematically illustrates a second variation on the configuration of FIG. 1.

FIG. 3B schematically illustrates a variation on the configuration of FIG. 3A.

FIG. 4 schematically illustrates a third variation on the configuration of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a vapor compression system with a compressor motor cooling subsystem 10 for a compressor 20 driven by a high speed motor 22 for HVAC applications. In one non-limiting example, the high speed motor 20 is a motor for a mini-centrifugal compressor. The system includes a condenser 30, an evaporator 40, and an expansion device 11 in fluid communication with the compressor 20. In order to provide cooling and lubrication to a high speed motor 22, a pressure rise generated by the compressor 20 provides liquid coolant from the condenser 30 to the motor 22 along a fluid flowpath 50 during full speed operations of the compressor 20. In the embodiment of FIG. 1, the liquid coolant cools and lubricates the motor 22, and is then provided to the evaporator 40 via the flowpath 58. Once in the evaporator 40, the coolant is evaporated, and provided to the compressor 20 in a vapor form along a vapor flowpath 60. The vapor flowpath 60 provides the evaporated coolant from the compressor to the condenser 30.

Once the compressor 20 has begun operating at a designed speed, the pressure buildup due to the operation of the compressor 20 is sufficient to drive the liquid coolant through the motor 20 and provide the cooling and lubricating effects. However, during initial startup there can be insufficient pressure to drive the liquid coolant, and a liquid coolant driving system 70 provides supplemental pressure to drive the liquid coolant through the motor 20. The liquid coolant driving system 70 can include multiple variations configured to generate the requisite compressor rise. FIGS. 2-4 describe exemplary embodiments of the liquid coolant driving system.

With regards to the liquid coolant flowpath 50, the flowpath 50 includes a first leg 52 that provides coolant from the condenser 30 to an input of a three-way valve 80. The first leg 52 includes the liquid coolant driving system 70. In alternative systems, the three-way valve 80 can be replaced with any other type of valve or regulator capable of regulating flow or flow switching between two input flow sources. Also included in the liquid coolant flowpath 50 is a second leg 54 that connects the condenser 30 directly to the three-way valve 80, or other flow switching device, to an expansion device 11, and to a liquid coolant input of the evaporator 40. As used herein a “valve switching device” generically refers to any flow switching device capable of switching a connection of an output between at least two inputs. A third leg 56 connects an output of the three-way valve 80 to a liquid coolant input of the motor 22, and a fourth leg 58 connects an output of the motor 22 to the output of the expansion device 11 in the second leg 54. After merging the coolant flows into the evaporator 40.

When the system 10 is initially switched on, the three-way valve 80 is set to receive liquid coolant from the condenser 30 via the liquid coolant driving system 70. The liquid coolant driving system 70 drives liquid coolant from the condenser 30 (via the first leg 52) to the motor 22, through the three way valve 80 and the expansion device 11, as the motor 22 begins operating thereby lubricating and cooling the motor 22.

Once the motor 22 is up to speed, and is generating sufficient liquid coolant feeding power due to the pressure buildup within the condenser 30, the three way valve 80 switches to receiving the liquid coolant from the second leg 54, and the liquid coolant driving system 70 is switched off. In this way, coolant is actively provided to the motor 22 directly from the condenser 30 through the second leg 54, the three way valve 80 and the third leg 56. Once provided to the evaporator 40, the liquid coolant evaporates and absorbs heat from another fluid that flows through the evaporator 40.

Operations of the motor 22, the three-way valve 80 and the liquid coolant driving system 70 are controlled via a controller 90. The controller 90 can be a dedicated cooling system controller, a motor controller, or any other controller capable of storing and implementing the control sequences described herein.

The liquid coolant can be any suitable low global warming potential refrigerant. In one example, the liquid coolant is the refrigerant R1233zd(E) (CHCl=CH=CF3) which has a very low direct global warming potential, a high cycle efficiency, is non-toxic and is non-flammable.

With continued reference to FIG. 1, FIG. 2 schematically illustrates an HVAC system 100, according to the example of FIG. 1, with the inclusion of a heat driven liquid coolant driving system 170. The heat driven liquid coolant driving system 170 is connected to an outlet of the condenser 130 via a check valve 172 positioned in a first leg 152 of a liquid coolant flowpath 150. The heat driven liquid coolant driving system 170 includes a reservoir 174, where liquid coolant is pooled. As used herein, the reservoir 174 refers to any component capable of storing liquid refrigerant, and can include oversized lines, a fluid tank, a portion of the condenser, etc.

In the embodiment of FIG. 2, an electric heater 176 (i.e. a device that generates heat using electricity) is disposed within the reservoir 174, or connected to the reservoir 174 such that the electric heater 176 raises the temperature of the liquid coolant within the reservoir 174 when activated. Alternative heat sources beyond those using electricity to generate heat can be utilized to the same effect with minor modifications to the described system. Raising the temperature in the reservoir 174 increases the pressure in the reservoir 174, and the increased pressure drives liquid coolant along the second leg 152 of the liquid coolant flowpath when a three way valve 180 connects the first leg 152 of the liquid coolant flow from the reservoir 174 to the third leg 156 of the liquid coolant flowpath.

In order to ensure sufficient pressure is built up within the reservoir 174, the electric heater 176 is activated prior to the activation of the motor 122. In some examples, this can include activation as many as 5 or 10 minutes prior to motor 122 activation and is governed by controller 90. The specific length of time by which the activation of the electric heater 176 must precede the activation of the motor 122 is determined by multiple factors including, but not limited to, the volume of coolant, the type of refrigerant, etc. Alternatively, activation of the motor is controlled by the pressure difference between the reservoir 174 and the evaporator 140.

With continued reference to FIGS. 1 and 2, FIGS. 3A and 3B illustrate an HVAC system 200 utilizing an electric pump 272 as the liquid coolant driver. In alternative examples, other means to drive the liquid coolant (e.g. electrohydrodynamics, etc.) are can be utilized to pump the liquid coolant without requiring an electrically driven pump 272. The HVAC system 200 is substantially identical to the systems described with regards to FIGS. 1 and 2, with the exception of the electric pump 272 being utilized to drive the liquid coolant in place of the heat driven liquid coolant driving system 170 of FIG. 2. The electric pump 272 can be included inside the base of the condenser 230, as shown in the example of FIG. 3A, or can be outside of the condenser 230 within the first liquid coolant flowpath 252. In both cases, the electric pump 272 receives electrical power via a connection to an external power source, such as a building electrical grid, or from an electrical connection to the HVAC system, and is activated by the controller configured to control the motor 220. The electric pump 272 can be any conventional electric pump having sufficient size and power to drive the liquid coolant.

Unlike the heat driven liquid coolant driving system 170 of FIG. 2, the pump driven system of FIG. 3A or 3B requires a minimal amount of lead up time after being activated and before the motor 22 can begin startup operations. By way of example, the lead-up time can be less than ten seconds. In some such examples, the lead-up time can be five seconds.

With continued reference to FIGS. 1-3B, FIG. 4 illustrates an HVAC system 300 having third variation on the liquid coolant driving system 70 of FIG. 1. The liquid coolant driving system of FIG. 4 utilizes a gravity fed reservoir 374 positioned physically above the motor, relative to a force of gravity, the reservoir is filled with liquid coolant from the condenser 330. The reservoir 374 is connected to an outlet of the condenser 330 via a check valve 372 positioned in a first leg 352 of a liquid coolant loop 350. When the three way valve 380 is switched to connecting the reservoir outlet to the motor 322, gravity causes the liquid coolant to pass through the motor 322, and allows the motor 322 to begin startup sequences. Due to the continuous application of gravitational forces, no lead-up time beyond the connection of the three-way valve 380 is required before the system of FIG. 4 is able to begin rotating.

In some examples, the gravity fed coolant system of FIG. 4 carries with it additional packaging restrictions, and the physical structure of the motor 322 is constructed to support the weight of the liquid coolant reservoir.

With reference now to all of FIGS. 1-4, after the initial startup the motor is cooled and lubricated by the liquid coolant provided directly from the condenser by switching the three-way valve to bypass the liquid coolant drive system. The liquid coolant flow is adjusted in order to maintain high performance evaporating cooling in the motor and low quality two phase refrigerant leaving from the motor.

It is further understood that any of the above described concepts can be used alone or in combination with any or all of the other above described concepts. Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention. 

1. A heating ventilation and air conditioning (HVAC) system comprising: a compressor comprising a low pressure input and a high pressure output, the compressor driven by a motor, the motor including a liquid coolant flowpath configured to cool and lubricate the motor and having a liquid coolant input and a liquid coolant output; an evaporator in fluid communication with the compressor, the evaporator including a liquid coolant input, and a vapor coolant output, the vapor coolant output being connected to the low pressure input of the compressor; a condenser in fluid communication with the evaporator and the compressor, the condenser including a vapor cooling input and a liquid coolant output, the vapor cooling input being connected to a high pressure output of the compressor; a first liquid coolant flowpath, including a liquid coolant drive system connecting the liquid coolant output of the condenser to the input of a valve switching device; a second liquid coolant flowpath connecting the liquid coolant output of the condenser to the liquid input of the evaporator and to a second input of the valve switching device; a third liquid coolant flowpath connecting an output of the valve switching device to the liquid coolant inputs of the motor; and a fourth liquid coolant flowpath connecting the liquid coolant outputs of the motor to the liquid coolant input of the evaporator.
 2. The HVAC system of claim 1, wherein the liquid coolant drive system comprises an electric pump.
 3. The HVAC system of claim 2, wherein the electric pump is disposed within a reservoir integrated into the condenser.
 4. The HVAC system of claim 2, wherein the electric pump is disposed within a reservoir exterior to the condenser.
 5. The HVAC system of claim 2 wherein the electric pump is disposed outside of the condenser.
 6. The HVAC system of claim 2, further comprising a controller controllably connected to the valve switching device, the electric pump and the motor.
 7. The HVAC system of claim 6, wherein the controller is configured to activate the electric pump at least five seconds prior to activating the motor.
 8. The HVAC system of claim 1, wherein the liquid coolant drive system comprises a liquid coolant reservoir.
 9. The HVAC system of claim 8, wherein the liquid coolant reservoir is disposed above the motor, relative to a force of gravity, such that a liquid coolant is gravity fed from said reservoir to said motor when the valve switching device is in a first state.
 10. The HVAC system of claim 8, wherein the liquid coolant reservoir includes an electric heater disposed within the liquid coolant reservoir.
 11. The HVAC system of claim 10, wherein the electric heater is controllably coupled to a controller, and the controller is configured to activate the electric heater at least 5 minutes prior to activating the motor.
 12. The HVAC system of claim 8, further comprising a one way valve disposed in the first liquid coolant flowpath between the liquid coolant output of the condenser and the input to the reservoir, and oriented such that liquid coolant flows from the condenser to the reservoir and is prevented from flowing from the reservoir to the condenser.
 13. The HVAC system of claim 1, wherein the liquid coolant flowpath includes a liquid phase R1233zd(E) (CHCl=CH=CF3) refrigerant.
 14. The HVAC system of claim 1, wherein the second liquid coolant flowpath includes an expansion device connecting the liquid coolant output of the condenser to the liquid input of the evaporator.
 15. The HVAC system of claim 1, wherein the first liquid coolant flowpath includes a check valve connecting the liquid coolant output of the condenser to the liquid coolant drive system.
 16. A method for operating a heating ventilation and air conditioning (HVAC) system comprising: driving a liquid coolant from a condenser to a compressor motor during a startup sequence of the compressor motor using a liquid coolant drive system, thereby cooling and lubricating the compressor motor; and drawing liquid coolant from the condenser to the compressor motor using a pressure differential between the condenser and an evaporator once the startup sequence has completed.
 17. The method of claim 16, wherein driving the liquid coolant comprises providing liquid coolant from the condenser to a reservoir and heating the liquid coolant in the reservoir, thereby increasing a pressure of the liquid coolant.
 18. The method of claim 16, wherein driving the liquid coolant comprises operating an electric pump disposed within the condenser.
 19. The method of claim 16, wherein driving the liquid coolant comprises operating an electric pump disposed between an outlet of the condenser and a liquid coolant inlet of the compressor motor.
 20. The method of claim 16, further comprising transitioning from driving the liquid coolant using the liquid coolant driving system to drawing liquid coolant from the condenser to the compressor motor using a pressure differential between the condenser and the evaporator in response to the compressor motor exceeding a rotational speed. 